1. Field of the Invention
This invention relates to a process and apparatus for welding small metal parts and components, and more particularly to a process and apparatus for micro arc welding of wires and foils as well as an alternate to soldering and spot welding.
2. Description of the Prior Art
The soldering and welding of wires, wires to plates or foils, and wires to semiconductor packages are ubiquitous processes in the manufacture and modification of electrical and electronic devices. "Spot welding" is extensively used to attach lamp and vacuum tube filaments to base wires and foils; soldering is almost universally used to make chip-to-package and substrate interconnections in electronic devices.
Four different technologies are currently available for electrical interconnection of chips to the substrates or packages. They are: wire bonding, flip-chip bonding, tape-automated bonding, and beam-lead bonding. All such processes routinely use environmentally harmful solders and chlorofluorocarbon (CFC) cleaning solvents. CFC's are ozone depletants and will be discontinued after 1995. Different alternative approaches are based on solvent substitute for CFC to laser and ultrasonic cleaning methods, and development of soldering processes which do not require cleaning. Other, general for soldering technologies and discussed in literature problems are connected with failures associated with mechanically and thermally induced stresses, surface contamination, the complex metallurgy of multiple layers, and thermal expansion mismatch between the chip and the solder and the solder and the substrate. In contact welding ("spot" welding) applications, reliability is the major problem, especially when refractory metals are welded together, as in lamp and vacuum tube applications.